This interesting result has one huge caveat: the engineers never documented their test procedure. The lack of documentation came to light when Clarence Ditlow, executive director of the Center for Auto Safety, used the Freedom of Information Act to demand access to the documentation.
So, the NHTSA will re-test the Toyota vehicles to determine whether its ETC malfunctions under high EM interference. It just might be the culprit and is something that would have been caught if Toyota management had spent more time and money on building physical protoypes of new vehicles instead of just building a virtual model inside a computer-aided-design (CAD) environment. The dangerous interaction between quite different components in the vehicle is something that CAD software does not model.
CAD software tends to be specific to a domain. There are CAD tools for designing the mechanical components like a throttle pedal. There are CAD tools for designing the electronic components like the ETC. However, CAD tools do not model how the EM emanating from the engine will impact the ETC. In order to assess that situation, you need a physical prototype and millions of man-hours of testing.